Method of coating ferrous strip material



June 9, 1936.

A. J. MARINO 2,043,549

METHOD OF COATING FERROUS STRIP MATERIAL Filed March 17, 1935 Quench/$6M,ZLJATTQR EY Patented June 9, 1936 UNITED STATES METHOD OF COATINGFERROUS STRIP MATERIAL Anthony J. Marino, Union City, N. J., assignor toGilby Wire Company, Newark, N. J., a corporation of New JerseyApplication March 17, 1933, Serial No. 661,303

4 Claims.

The invention relates to a method of coating ferrous strip material, andmore particularly to the application of a thin coating of carbon to thesurfaces of a base strip or strand without so hardening it as to impairits properties of malleability or ductility.

In the production of thermionic tubes for use in radio sets, the use ofa bright metal anode or plate has been found to result in overheating ofthe anode or plate, with a consequent interference with the constantcapacity of the tube, due to the tendency of the electrons emited fromthe cathode to adhere to, or accumulate upon, the surface of the plate.To overcome this difliculty, attempts'have been made to apply a coatingof carbon to nickel or nickel alloys, but the methods employed are suchas to require excessively high temperatures, and the product not only isso expensive as to materially increase the cost of the tubes, butcontains other objectionable characteristics so far as reliability inthe action of different tubes is concerned.

Attempts to apply a carbon coat to soft iron or steel strip or wirehave, prior to my invention, been unsuccessful because, by the methodsemployed, the application of the carbon to the base material hasresulted in the chemical modification of the structure of the ferrousmaterial at its surface resulting in the hardening thereof in a,

manner to preclude the subsequent forming or drawing operationsnecessary to give to the material the form required to adapt it for usein an electron tube, or for other purposes.

I have dlscc ered that a permanent, thin coating of carbon may beapplied to a base consisting of a strip or wire of soft iron or steel bysubjecting it to an elevated temperature in the presence of an oxidizingmedium resulting in the oxidation oi the surface of the iron or steel,subsequently reducing the temperature of the ferrous material of thestrip or wire, and then subjecting the oxidized strip or wire to anelevated temperature in the presence of a gas rich .in carbon.

In the practice of the process, I have found it necessary, to avoid thehardening of the surface of the iron or steel, to keep within a narrowtemperature range during the oxidizing and the carbonlzation stages, andto control the temperatures attained by the base strip or wire by thespeed at which the same travels while subjected to the elevatedtemperatures above referred to.

The success of the method or process is dependent largely upon thefactors of time and temperature during, and at which the oxidation stepand the carbonization step are performed. The

proper temperatures and the proper time intervals ensure a high degreeof uniformity and permanency in the carbon coating throughout the entirelength of the strip or wire without any appreciable hardening effectupon the material of the base strip or wire.

The invention consists primarily in a method of coating ferrous stripmaterial consisting in subjecting a strip or wire of soft iron or steelto a temperature of substantially 1200" F. in the presence of 'anoxidizing medium for a time interval of substantially four minutes, aircooling the strip or wire for an interval of substantially four minutes,and then subjecting the oxidized strip or wire to a temperature ofsubstantially 1100 F. in the presence of a gas rich in carbon for a timeinterval in excess of four minutes; and in such other novel steps andpractices as are hereinafter set forth and described, and moreparticularly pointed out in the claims hereto appended.

In the accompanying drawing, I have illustrated diagrammatically themethod of the invention.

Inthe drawing, it indicates a coil of strip or wire of iron or steel ofsoft drawing stock. The wire from the coil 0. passes through a furnace bin which atmospheric air is permitted to circulate freely. After leavingthe furnace b, the strip or wire from the coil a passes in the presenceof an oxidizing medium through a low temperature zone 0, until it entersa carbonizing furnace d charged through a pipe e with a gas rich incarbon. The furnace d is completely closed, except for substantially gastight roller gates ,f and g at the points where the strip or wire aenters and leaves the furnace. Beyond the furnace b is a quenching tankh for cooling the completed product before collecting it upon the rewindreel i, which may be continuously rotated in any desired manner, as bythe speed reducing mechanism a, to ensure a continuous rate of travel ofthe strip or wire a. Guide rollers k, k 10 h it, and k are provided toensure a proper run of the strip or wire. a

By reference to the foregoing description, it will be noted that themethod is a continuous one, and may be carried on in a manner to ensuresubstantially uniform time intervals during each step of the method asto every portion of the length of strip or wire. This results inuniformity throughout the product, which is highly desirable from thestandpoint of manufacturers employing the product.

Referring more particularly to the procedure followed in the practice ofthe method of the invention, a temperature of approximately 1200 F. ismaintained in the oxidizing furnace b, and a relatively lowertemperature, substantially 1100 F. is maintained in the carbonizingfurnace d. The length of the oxidizing furnace b is approximately 4feet; the length of the low temperature zone intermediate the furnaces band dis approximately 4 feet, and the length of the carbonizing furnaced is approximately twice that of the oxidizing furnace.

The means actuating the rewind reel is so geared as to impart asubstantially uniform speed to the strip or wire of one foot per minute.Any desired mechanical expedients for ensuring a uniform speed of thestrip or wire may be employed.

The length of the furnaces and the speed of the strip or wire are timefactors with which, at the temperatures stated, a thin strip,approximately .005of an inch in thickness, is oxidized and coated withcarbon to the desired extent.

Oxidizing apparently occurs while the strip or wire is passing throughboth the furnace b and the low temperature, air cooling zone 0.

The desired reactions result from the temperatures to which the materialis subjected and the time during which they are subjected to suchtemperatures. These factors are not constant, to the extent that theymust be varied in proportion to the cross sectional area of thematerial. This variation may be secured with materials of greater crosssectional area than stated by using furnaces of greater length, byreducing the speed of the material or by increasing the temperature inthe furnaces within a small range. I have herein given an example oftime and temperatures which I have found give excellent results when thematerial being coated is substantially pure commercial, or Swedish iron.

The oxidizing medium used is ordinary atmospheric air. In the furnace d,I may use natural gas, producer gas or other gases rich in hydrocarbons,which, if desired, may be enriched as compared with the normal productin the manner usually employed for producing enriched gas, to wit: theintroduction of hydro-carbons during the production or consumption ofthe gases.

Water may be used in the quenching bath h, the purpose of this bathbeing merely to reduce the temperature of the material before re-coilingsame.

The time and temperature factors are such as to ensure the deposit of apermanent carbon coating on the surface of the base strip or wire a,which apparently is of uniform thickness and actually incorporated inthe structure of the base at the surface thereof. There is no reductionhaving any appreciable hardening effect upon the iron of the base, andthe completed'product has substantially the same inherent properties ofmalleability or ductility as the untreated strip or wire. It may beformed or drawn into any desired shape without the development ofsurface cracks or checks.

The temperature employed during the carbonization step is vital to thesuccessful practice of the method of the invention, although thistemperature is subject to slight variation, as herein referred to, solong as the conditions are such as to ensure a. temperature of theferrous base which is substantially that resulting from the exampleherein stated. During oxidation alone there can be no material hardeningof the base. During carbonization there would be such a hardaoaaseeening, if excessively high temperatures were employed.

The word permanent is used herein to mean that the major portion of thecoating is so incorporated in the structure of the base at the surfacethereof as to resist separation therefrom except by abrasion. Lightbumng will have no effect upon the coating, except the removal of asmall percentage of the surface carbon.

While I have described the use of the material produced by the method ofthe invention in the production of thermionic tubes, it is obvious thatthe uses to which the product is put are immaterial to the invention.

The temperatures attained by the ferrous base are controlling in thepractice of the method, and since they are the resultant of the time andtemperature factors herein referred to, variation of these temperaturesas herein referred to are permissible so long as the resultanttemperatures are n substantially constant.

Because of the low temperature developed in the carbonizing furnace orchamber, the quenching bath will have no effect in hardening the surfaceof the product.

Having described the invention, what I claim as new and desire to haveprotected by Letters Patent, is:

1. The herein described method of coating ferrous strip materialconsisting in subjecting a strip or wire of soft iron or steel to atemperature of substantially 1200" F. in the presence of an oxidizingmedium for a time interval of substantially four minutes, air coolingthe strip or wire for an interval of substantially four minutes, andthen subjecting the oxidized strip or wire to a temperature ofsubstantially 1100 F. in the presence of a gas rich in carbon for a timeinterval in excess of four minutes.

2. The herein described method of coating ferrous strip materialconsisting in subjecting a strip or. wire of soft iron or steel to atemperature of substantially 1200 F. in the presence of an oxidizingmedium for a time interval of substantially four mintues, air coolingthe strip or wire for an interval of substantially four minutes,thensubjecting the oxidized strip or wire to a temperature ofsubstantially 1100 F. in the presence of a gas rich in carbon for a timeinterval in excess of four minutes, and thereafter passing the strip orwire through a quenching bath.

3. The herein described method of coating ferrous strip materialconsisting in continuously roving a strip or wire of soft iron or steelsuccessively through an oxidizing medium maintained at substantially atemperature of 1200 F. for a time interval of substantially fourminutes, through an air cooling zone for a time interval ofsubstantially four minutes and through a gas rich in hydro-carbonmaintained at a temperature of 1100 F. for an interval of substantiallyeight minutes.

4. The herein described method of coating ferrous strip materialconsisting in continuously moving a strip or wire of soft iron or steelsuccessively through an oxidizing medium maintained at substantially atemperature of 1200" F. for a time interval of substantially fourminutes, through an air cooling zone for a time interval ofsubstantially four minutes and through a gas rich in hydro-carbonmaintained at a temperature of 1100 F. for an interval of substantiallyeight minutes, and passing the strip or wire through a quenching bath.

ANTHONY J. MARINO.

